Electron paramagnetic resonance +reductant

Davydov, R., Kuprin, S. Graslund, A., and Ehrenberg, A. 1994. Electron paramagnetic resonance study of the mixed-valent diiron center in Escherichia coli ribonucleotide reductase produced by reduction of radical-free protein R2 at 77 K. Journal of the American Chemical Society 116 11120-11128. 

R. Nilsson, F.M. Pick, and R.C. Bray, Electron paramagnetic resonance studies on reduction of oxygen to superoxide by some biochemical systems. Biochim. Biophys. Acta. 192, 145-148 (1969). 

The FeMo cofactor (or M center) in the MoFe-proteinis in the native paramagnetic M state. Reduction of the MoFe-protein by the Fe-protein results in the reduction of FeMo-co from the M state to the M state at a potential estimated to be less than —0.465 V (NHE). The electron paramagnetic resonance (EPR) silent M state is only transiently produced during catalysis, and relaxes to the M state when catalysis stops. The intimate consequences of the M state reduction are not precisely known. A more oxidized diamagnetic state may also be generated (M ) at —0.042 V but its biological relevance is unclear [9]. 

Silacyclobut-l-yl, 1-methylsilacyclobut-l-yl, and 3-methylsilacyclobut-l-yl radicals were prepared by 7-irradiation of the corresponding silanes in adamantane matrices at 77 K. Electron paramagnetic resonance (EPR) studies show that the radicals have a nonplanar ring <1988JOM(341)273>. The reduction of phenylsilacyclobutanes with potassium gave anion radicals, and their EPR spectra were recorded at — 75 °C (Table 5) <1983ZOB1315>. 

Microsomal reduction of chromium(VI) can also result in the formation of chromium(V), which involves a one-electron transfer from the microsomal electron-transport cytochrome P450 system in rats. The chromium(V) complexes are characterized as labile and reactive. These chromium(V) intermediates persist for 1 hour in vitro, making them likely to interact with deoxyribonucleic acid (DNA), which may eventually lead to cancer (Jennette 1982). Because chromium(V) complexes are labile and reactive, detection of chromium(V) after in vivo exposure to chromium(VI) was difficult in the past. More recently, Liu et al. (1994) have demonstrated that chromium(V) is formed in vivo by using low-frequency electron paramagnetic resonance (EPR) spectroscopy on whole mice. In mice injected with sodium dichromate(VI) intravenously into the tail vein, maximum levels of chromium(V) were detected within 10 minutes and declined slowly with a life time of about 37 minutes. The time to reach peak in vivo levels of chromium(V) decreased in a linear manner as the administered dose levels of sodium... 

A reaction mechanism for the above reactions was proposed which consists of initial formation of the copper precursor complexes of Fig. 3 (without coordinated phenolate), coordination of phenolate, electron transfer from phenolate to Cu2+ and subsequent reduction to Cu1+ with formation of a phenoxy radical, and reoxidation of Cu1+ to Cu2+ with oxygen. Various copper(II) catalysts having different stereochemistries (octahedral or tetrahedral coordination) due to coordination of amines like pyridine (Py) or acetate (OAc) groups in different ligand sites were observed by NMR and electron paramagnetic resonance techniques. 

Electron paramagnetic resonance (EPR) spectroscopy is a powerful technique to explore the electronic state of iron complexes. EPR spectroscopy of the non-heme iron component in the electron transfer system of mitochondria has been extensively used and discussed by Beinert (9), who showed that this type of iron has a so-called g = 1.94 type signal upon reduction. Consideration of the EPR spectrum of adrenodoxin has been described previously (68). 

Hanley, J., Sarrou, J., and Petrouleas, V. (2000) Orientation of the Mn(II)-Mn(II) dimere wwhich result from the reduction of the oxygen-evolving complex of Photosysem II by NO an electron paramagnetic resonance study, Biochemistry 39, 15441-15445. 

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